a HSN TECHNICAL NOTE - HSN TN009 ADN2841 OPTICAL EVALUATION KIT Introduction: This Technical Note describes the ADN2841 laser diode driver Rev. C1 evaluation kit. The evaluation kit is a demonstration board that provides optical evaluation of the ADN2841. This document describes how to configure the board in order to operate the part optically. The document contains the following information: * Board Description. * Quick Start for optical operation. * Description of board settings. * General Notes. * Component List. * Schematic of board. * Board Layout Information * Silkscreen Image of board * Optical Eyes Board Description: The ADN2841 is a dual loop 155Mbs to 2.7Gbps laser diode driver. To use the board in an optical configuration, a suitable laser diode driver must be soldered onto the board. The monitor photo diode, MPD, current is fed into the ADN2841 to control the average power and extinction ratio. The ADN2841 uses automatic power control, APC, to maintain a constant average power over time and temperature. The ADN2841 uses closed loop extinction ratio control to allow optimum setting of extinction ratio for every device. This board is configured for lasers in Minidil packages only. LEDs for Power Supply, DEGRADE, and FAIL are made available for monitoring purposes. Power to the evaluation circuitry is -5V only! Quick Start for Optical Operation: To ensure proper operation in the optical configuration, verify the following: 1. Jumpers K3 & K4 are connected to A, Jumpers K2 & K5 are connected to B. 2. If the input data is clocked it is necessary to enable the clock select pin (CLKSEL). CLKSEL is enabled by connecting K4 to B. If the clock inputs are not used, or the input data is not latched, connect K4 to A. 3. The power supply is diode protected to ensure the device is not damaged if a +5V power supply is accidently connected. The user may connect Jumper K1 (short circuit) and power up the board by applying -5V to the POWER input SMA, J3. If Jumper K1 is not connected then the user should make the power supply sufficiently negative to enure that the DUT supply is -5V. The actual DUT supply can be measured at the anode of D1. REV. D Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. REV. D Oct. 2001 One Technology Way, P.O. Box MA 02062-9106, U.S.A. Tel: Fax: 617/326-8703 9106, Norwood. 617/329-4700 HSN TECHNICAL NOTE -HSN TN009 ADN2841 EVALUATION KIT 4. Apply a differential signal, typically 500mV, to J6 and J7 (DATAN and DATAP). Single ended operation may result in a degraded eye 5. If the clock select pin is enabled by K4, apply a differential clock signal, typically 500mV, to J4 and J5 (CLKN and CLKP). 6. The optical eye and switching characteristics of the ADN2841 may be observed using a digital communications analyser which has an optical input channel with the required bandwidth. 7. The bias and modulation currents can also be monitored by observing Ibmon and Immon respectively. Ibmon and Immon are both a 1:100 ratio of Ibias and Imod. Both are terminated with resistors and so can be viewed at Test Points T3 and T4 using a voltmeter or oscilloscope. 8. To establish the desired average power and extinction ratio the user should follow the below procedure: With the power supply turned off adjust potentiometers R20 (ERSET) and R21 (PSET) to approx 20k. With the evaluation board powered on reduce the value of potentiometer R21 to establish the desired average optical power. Potentiometer R20 can then be reduced in value to increase the modulation current, and hence increase the extinction ratio. The bias current will decrease as the modulation current increases. The bias and modulation currents can be monitored using IBMON and IMMON. When adjusting the extinction ratio the user should allow adequate time for the eye to settle. The allowable resistance range at the Power Set Input (PSET), the Extinction Ratio Set Input (ERSET), and the Alarm Set (ASET) is between 1Kohm and 25Kohm. Resistors R31-R33 ensure that the resistance at these nodes never falls below the minimum allowable value. If the node resistances increase above 25Kohm the ADN2841 may not operate within its specifications. REV. D, Oct 2001 2 HSN TECHNICAL NOTE -HSN TN009 ADN2841 EVALUATION KIT Description of Board Settings: COMPONENT NAME J3 POWER J1 IDTONE J4 CLKN J5 CLKP J6 DATAP J7 DATAN T1 IMPDMON T2 IMPDMON2 T3 IBMON T4 IMMON R19 ASET POTENTIOMETER R20 ERSET POTENTIOMETER R21 PSET POTENTIOMETER K1 K1 K2 K2 K3 K3 K4 K4 K5 K5 REV. D Oct 2001 FUNCTION -5V power input to board Idtone input. Clkn input. Clkp input. Datap input. Datan input. IMPD Current Mirror Monitor MPD2 Current Mirror Monitor Bias Current Mirror Monitor Modulation Current Mirror Monitor Adjusts bias current threshold for disable and fail alarms. Adjusts for slope efficiency. Adjusts the mpd current and thus the average power. Jumper to bypass supply protection diode. Jumper for LBWSET Jumper to exercise ALS Jumper for CLKSEL Jumper for IDTONE 3 HSN TECHNICAL NOTE -HSN TN009 ADN2841 EVALUATION KIT COMPONENT QTY R19, R20, R21 3 D1 1 D2, D3, D4 3 C4-C12, C16-C18 8 C2 1 C13, C14 2 Q3, Q4 2 C1 1 C15 1 R10, R15, R18 3 R3 1 R5 1 R2 1 R1, R16, R17, 3 R6 1 R31-R33 3 R11, R12, R13, R14 4 R25*, R26, R27*, R28*, R29 5 K1-K5 4 J1, J3-J7, J8* 7 U1 1 U2* 1 L1, L2 2 DESCRIPTION 50k trim potentiometer Supply Protection Diode (IN4001) SMD LEDs 10nF capacitor 220uF capacitor 1F capacitor (Loop Bandwidth Setting) Transistor (SOT23) 22uF 1pF 10k resistor. 10 Ohm resistor 100 Ohm Resistor 24 Ohm resistor 330 Ohm resistor. 1k Ohm resistor 820 Ohm resistor. 1k5 Ohm resistor. 0 Ohm resistor Pin header jumper sockets SMA connector. ADN2841 Laser Diode - Not supplied by Analog Devices 10H inductor *Signifies components which are not populated REV. D, Oct 2001 4 HSN TECHNICAL NOTE -HSN TN009 ADN2841 EVALUATION KIT Figure 1. Schematic of Board REV. D Oct 2001 5 HSN TECHNICAL NOTE -HSN TN009 ADN2841 EVALUATION KIT BOARD LAYOUT Figure 2. PC Component Side Figure 3. PC Ground Plane Figure 4. -5V Power Plane Figure 5. Solder Side REV. D, Oct 2001 6 HSN TECHNICAL NOTE -HSN TN009 ADN2841 EVALUATION KIT Figure 6. Silkscreen Image Figure 8. Filtered 2.5Gbs Optical Eye. Average Power = -3dBm, Extinction Ratio = 9dB. Eye obtained using a Mitsubishi FU-445-SDF Figure 7. Unfiltered 2.5Gbs Optical Eye. Average Power = -3dBm, Extinction Ratio = 9.5dB. Eye obtained using a Mitsubishi FU-445-SDF. REV. D Oct 2001 7 HSN TECHNICAL NOTE -HSN TN009